What are specific
types of coastal ecosystems and how is their biological productivity being
threatened?

What human hazards
are associated with living near coasts?

How can we minimize
or mitigate risks to human welfare and coastal resources?

Types of
Coastal Zones

Coastal
zones include many types of environments:

Upwelling
areas were described in a previous lecture. They are highly productive
because nutrient rich water from depth reaches the surface where ample
sunlight fuels primary production.

Coral
reefs are amongst the most impressive and diverse, as well as productive
structures on earth. Although we will not discuss reefs in detail,
you should be aware that coral reefs face a variety of
serious
threats. Reefs of the Tropical
Americas are at particularly high risk.

About 58 percent of the world’s reefs
are at risk of degradation because of coastal development, destructive
fishing and pollution from inland runoff from deforestation and farming.

Coastal reefs of Southeast Asia are
most threatened, with more than 80 percent at risk, primarily from coastal
development and fishing.

In the United States, most reefs face
some risks, with all reefs off Florida facing potential degradation because
of coastal development and farming-related pollution.

Two-thirds of the Caribbean reefs are
in jeopardy, including high risks to reefs off Puerto Rico, the U.S. Virgin
Islands, Jamaica and Barbados. The principal culprits are overfishing and
pollution including high levels of nutrients that cause algae growth.

Slight warming of surface waters due
to climate change can cause coral bleaching and death

The Coastal
shelf is characterized by shallow (200-m depth) water, and extends
50 (Cape Hatteras) to 150-km (Cape Cod) offshore. The Shallow depth
allows re-suspension of nutrients due to storms, and so biological productivity
usually is high.

Estuaries
form where freshwater from rivers and streams flows into the ocean, mixing
with the salty sea water. Important examples include San Francisco
Bay, Puget Sound, Chesapeake Bay, Boston Harbor, and Tampa Bay. Estuaries
act as a natural buffer between the land and ocean, absorbing flood waters
and dissipating storm surges. Often they exhibit vertical stratification,
with outward-flowing freshwater resting on a layer of denser salt water
along the bottom.

Salt marshes
line much of the Atlantic Seaboard. These highly productive ecosystems
serve as nursery grounds for diverse fish and shellfish, and habitat for
birds and other wildlife. They trap sediments and nutrients as well.
The cord grass Spartina is the most important plant in many easter
seaboard saltmarshes.

Mangroves
are composed of mangrove trees that have specially adapted aerial and salt-filtering
roots and salt-excreting leaves that enable them to occupy the saline wetlands
where other plant life cannot survive. Mangrove is not a taxonomic
category, but a diverse group of salt-tolerant plants. They provide
habitat and stabilize currents, allowing many organisms to dwell amongst
them.

Coastal
Shore and Barrier Islands

Scenic and
rich in wildlife, coastal regions have high recreational value.
Roughly 300 barrier islands occur on Atlantic and Gulf Coasts.
Extremely dynamic land masses, they are retreating landward in response to
rising sea levels

Figure 3.
A highly developed barrier island (left) exposes large numbers of people
to meterological hazards. An undeveloped barrier island (right) exposes
no humans to risk and protects a natural feature.

What
makes Coastal Zones Biologically Productive?

As
we will learn in the lecture on fisheries,
most of the the harvestable production of the seas comes from coastal areas
and upwelling areas (which are coastal as well). The open ocean is
vast, and due to its large extent, contributes the bulk of the oceans primary
production, but only a fraction of the harvestable fish and shellfish.

Why are coastal
zones productive? River export of nutrients, localized nutrient upwelling,
water column mixing and resuspension of nutrients during storms and ample
light for photosynthesis, all contribute to high productivity in coastal
zones.

Threats to Coastal Zones

Globally,
coastal zones are stressed by population growth. Population pressures
include increased solid waste production, polluted urban runoff, and loss
of green space and wildlife habitat.

Figure 4.
50% of world’s population lives within 6 km of the sea. Some 14 of
15 largest mega-cities are coastal.

Coastal zone
population trends document the human influx to these areas. About
53% of the US population resides along its coastal fringe (excluding Alaska),
although coastal counties account for only about 17% of the land area in
contiguous U.S. Fourteen of 20 largest U.S. cities are located in
coastal zone.

Michigan’s
Coastal Zone is amongst its most valuble resources. With 3,288 miles
of coast, Michigan has the world’s largest freshwater coastline.
The Department of Natural Resources of Michigan manages coastal activities
such as shipwreck salvaging, building piers and marinas, and development.
Tourism, boating, fishing, commercial shipping, agriculture and manufacturing
are the State’s largest coastal industries.

The prevailing
strategy adopted for preservation of these ecosystems is that of Integrated
Coastal Management, which includes integration across levels of authority
(federal, state, regional, local), economic sectors (recreation, agriculture,
industry, energy), traditional disciplines (science, engineering, law,
etc.), and management tasks (wetlands, restoration, fisheries, etc.). Funding
is provided to coastal states that take on a coastal management effort
for wetlands, lagoons, reefs, and other habitats. Improved recreational
use, minimization of property damage from coastal hazards, and intergovernmental
cooperation are also emphasized. Thirty-two states have approved plans
for adopting the Coastal Zone Management Act by developing new standards
in coastal management. The Office
of Ocean and Coastal Resource Management works to effectively manage
multiple uses of the nation's coastal and ocean resources.

Extreme events
of nature are natural, and not human hazards until humans find themselves,
or place themselves, in the path of storms and hurricanes.

The increased
population density along coasts increases risks to human safety and property.
Annual, nationwide disaster losses were $4.5 billion in 1970; today direct
loss estimates are $10-20 billion dollars. Of an estimated $500 billion
total losses 1975-1994, 80% were caused by meterological events and only
17% were insured.

Figure 6. This coastal residence,
although guarded by sand bags, was totally destroyed by Hurricane Fran.

Reducing the
Impacts

To minimizing
the impacts of coastal zone hazards requires preparedness and a better
informed public, including improved capability in:

predicting hazard
events and impacts

mobilizing the
public to evacuate or shelter

reducing overall
vulnerability of people and property

Figure 7. Cost of Hurricanes Damage, in billions of dollars (left panel) and
Loss of Life (right panel). While the cost of natural disasters are rising
sharply (left), loss of life is falling sharply (right).

Threats
to Coastal Fisheries

While over-harvesting
is a serious threat to many fisheries, additional human threats exist.
They include destruction of estuaries and marshes where much reproduction
occurs and juveniles spend their early lives, shifts in biological activity,
often due to nutrient enrichment, and the development of oxygen-depleted
regions, also due to nutrient enrichment.

Nutrients include
nitrogen, phosphorus, and other elements that stimulate plant growth.
Excessive nutrients leads to high levels of plant growth, termed eutrophication.
Lake Erie was famous in the 1970's for this problem. All of this
biological production eventually is consumed by microbes and their metabolic
activities, which can deplete the oxygen available to very low levels.

Hypoxia is
defined as < 2-3 mg/L O2 and anoxia is 0 mg/L O2.
Sea water is often 6-8 mg/L O2, and organisms are stressed by
low oxygen levels. The de-oxygenated zone is usually confined to
the bottom waters, and if severe, is devoid of most life. While fish
probably leave dead zones, less mobile, bottom-dwelling organisms may be
killed.

Dead zones
(hypoxic or anoxic waters) are known from a number of locations.
Chesapeake Bay and Gulf of Mexico dead zones have attracted much attention
due to their size, and the loss of valued biological resources.

In order to limit nutrient loading
to aquatic ecosystems, we need to identify where the excess nutrients originate.
We do this using the mass balance approach.

inputs = outputs +/- storage

The inputs of
N include atmospheric NOx from internal combustion engines and
coal-fired power plants, fertilizer, and sewage. Outputs of N include
export from river mouths (which causes coastal eutropication and dead zones),
and biological processing en route (which helps reduce the N-load to the
seas). Storage occurs in channel sediments and floodplains.
The mass balance approach demonstrates that fertilizer is the source of
the increased nitrogen delivered to the sea by large rivers.

Chesapeake
BayThe
Chesapeake Bay is the largest estuary in the U.S., encompassing 64,000
mi2. Its near-area population is home to 15 million people.
"The Bay" is of enormous value. It is the largest source of oysters
in the U.S. and largest producer of blue crab in the world. The Bay
is also important for shipping, recreation and fishing. Unfortunately,
it receives waste from point and non-point sources throughout a huge drainage
basin.

The Gulf of
Mexico now experiences an anoxic zone twice the size of the entire Chesapeake
Bay. This dead zone has been devastating to bottom organisms, including
its famous shrimp, and drives fish away. The anoxic zone was first
discovered in the 1970's, and has grown greatly in size. Are excessive
nitrogen loads from the Mississippi River responsible? If so, what
accounts for the increase in nitrogen in the river and what can be done
about it?

Mass balance
calculations attribute 80% of Mississippi’s nitrogen load to fertilizers,
originating in the agricultural heartland of the USA. Nitrate loads
of the Mississippi are three times higher than in the 1950’s, and chemical
fertilizer use in the Midwest has tripled over this period. The evidence
seems clear. Fertilizer use in the upper Mississippi Basin is the
culprit. Iowa farmers and Louisiana shrimpers are in conflict.
However, the farming communities of the Midwest are not necessarily in
agreement.

What are possible
solution to excess nutrient export?

Use less fertilizer:
low cost entices farmers to over-fertilize, hoping for a good year

Use nitrogen-fixing
crops

Retain wetlands
and riparian buffers, sites of denitrification and nutrient uptake by plants